| Biography | |
|---|---|
 Prof. Osman Adiguzel Firat University, Elazig, Turkey, Turkey |
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| Title: Shape Memory Phenomenon and Crystallographic Aspects of Reversibility in Shape Memory Alloys | |
| Abstract:
Shape memory alloys take place in a class of advanced smart materials, by exhibiting shape reversibility. These alloys exhibit a peculiar property called shape memory effect, which is characterized by the recoverability of two certain shapes of material at different conditions. This phenomenon is initiated with thermomechanical processes on cooling and deformation processes and performed thermally on heating and cooling, with which shape of materials cycles between original and deformed shapes in reversible way in bulk level. Therefore, this behavior can be called thermoelasticity.
Thermoelasticity is governed by crystallographic transformations, thermal and stress induced martensitic transformations on cooling and stressing, and reverse austenitic transformation on heating. Thermal induced martensite occurs on cooling with cooperative movement of atoms in <110 > -type directions on the {110}-type plane of austenite matrix in self-accommodating manner, by means of lattice invariant shear, along with lattice twinning and ordered parent phase structures turn into twinned martensite structures. Twinned structures turn into detwinned martensite structure with deformation, by means of stress induced martensitic transformation.
These alloys exhibit another property, called superelasticity, which is performed by stressing and releasing the material in elasticity limit at a constant temperature in the parent phase region, and shape recovery occurs on releasing. Superelasticity exhibits ordinary elastic material behavior, but it is performed in non-linear way; loading and unloading paths are different at the stress-strain diagram, and hysteresis loop refers to energy dissipation. Superelasticity is also governed by stress induced martensitic transformation and ordered parent phase structures turn into detwinned martensite structures with stressing. However, lattice twinning and detwinning reactions play important role in martensitic transformations.
Copper based alloys exhibit this property in metastable β-phase region, which has bcc-based structures. Lattice invariant shears are not uniform in these alloys, and the ordered parent phase structures undergo the non-conventional layered structures. The long-period layered structures can be described by different unit cells as 3R, 9R or 18R depending on the stacking sequences on the close-packed planes of the ordered lattice.
In the present contribution, electron diffraction and x-ray diffraction studies performed on two copper- based CuZnAl and CuAlMn alloys. Electron diffraction patterns and x-ray diffraction profiles exhibit super lattice reflections in martensitic condition. Specimens of these alloys aged at room temperature in martensitic condition, and a series of x-ray diffractions were taken duration aging at room temperature. Reached results show that diffraction angles and peak intensities change with aging time at room temperature. Some of the successive peak pairs providing a special relation between Miller indices come close each other, and this result leads to the rearrangement of atoms in diffusive manner.
Keywords: Shape memory effect, martensitic transformation, thermoelasticity, superelasticity, lattice twinning, detwinning. | |
| Biography:
Dr. Osman Adiguzel graduated from Department of Physics, Ankara University, Turkey in 1974 and received PhD- degree from Dicle University, Diyarbakir-Turkey. He studied at Surrey University, Guildford, UK, as a post doctoral research scientist in 1986-1987, and his studies focused on shape memory alloys. He worked as research assistant, 1975-80, at Dicle University and shifted to Firat University in 1980. He became professor in 1996, and he has been retired due to the age limit of 67, following academic life of 45 years.
He published over 80 papers in international and national journals; He joined over 120 conferences and symposia in international and national level as Plenary Speaker, Keynote Speaker, Invited speaker, speaker or Poster presenter. He served the program chair or conference chair/co-chair in some of these activities. In particular, he joined in last six years (2014 - 2019) over 60 conferences as Speaker, Keynote Speaker and Conference Co-Chair organized by different companies in different countries.
Additionally, he retired at the end of November 2019, and contributed with Keynote/Plenary Speeches over 120 Virtual/Webinar Conferences, due to the coronavirus outbreak in three year of his retirement, 2020 and 2022.
Dr. Adiguzel served his directorate of Graduate School of Natural and Applied Sciences, Firat University in 1999-2004. He supervised 5 PhD- theses and 3 M. Sc theses. He is also technical committee member of many conferences. He received a certificate which is being awarded to him and his experimental group in recognition of significant contribution of 2 patterns to the Powder Diffraction File – Release 2000. The ICDD (International Centre for Diffraction Data) also appreciates cooperation of his group and interest in Powder Diffraction File.
Scientific fields of Dr. Adiguzel: Shape memory effect and displacive phase transformations in shape memory alloys and other alloys, molecular dynamics simulations, alloy modeling, electron microscopy, electron diffraction, x-ray diffraction and crystallography.
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